It is known to provide a fuel tank in a vehicle to hold a reservoir of fuel to be used by an engine of the vehicle. It is also known to provide a fuel pump assembly inside the fuel tank to pump fuel from the reservoir to the engine. Typically, the fuel pump includes a one way check valve configured to allow fuel to exit the fuel pump or fuel tank via a fuel line under certain conditions. Generally, a forward flow check valve consists of a checking device, typically a plunger, such as a pintel having a seal, and a seat that when in contact form a leak proof seal. The pintel and seal are forced against the seat with a spring that provides the proper force to maintain pintel and seal to seat contact during no flow and low-pressure forward flow conditions. This force prevents flow from exiting the fuel tank when the vehicle fuel line is removed or when a sufficient amount of pressure is not in the line.
During a vehicle shut down pressure in the fuel delivery system past or downstream from the check valve of the fuel pump may increase due to heating of the fuel in the line, which may occur due to heat radiated from the engine after it is shut down. In order to provide a release for this pressure in a vehicle shut down situation a release valve can be positioned to provide the pressure release when a threshold value has been reached. The pressure release valve will allow fuel to be released back into the fuel reservoir. However, such a pressure release downstream from the check valve will cause air to be allowed into the fuel circuit due to the releasing of fuel under pressure. As the fuel and air in the line cool, a vacuum can be created in the fuel circuit downstream from the check valve resulting from the reduction in volume of liquid fuel. Moreover, if the vacuum in the fuel circuit is not sufficient to overcome the pressure setting of the check valve (e.g., spring closing force) a loss of fuel or fuel pressure may occur in the circuit after the check valve. Such a loss of fuel or pressure will have to be overcome during a starting sequence when the pump again starts to pump fuel into the circuit. Overcoming this loss of fuel or pressure in the circuit may cause the starting sequence to take longer than a starting sequence wherein there is no loss of fuel or pressure in the circuit.
In order to ensure that fuel system pressure is maintained at a certain pressure in the fuel rail during a vehicle shut down, a fuel pressure regulator can be modified to have an expensive lapping process to ensure that a desired fuel pressure is maintained in the fuel rail during vehicle shut down. However, the pressure release of the regulator will be at the same value as the regulator is designed to provide during pumping of the fuel in an engine running or starting sequence.
Accordingly, it is desirable to maintain a desirable fuel pressure in the fuel rail during vehicle shut down without modifying the fuel pressure regulator and limiting the number of valves positioned in the circuit.